DESCRIPTION: A vital characteristic of living systems is their ability to perform efficient energy conversion. Biological energy transduction (ET) is the ensemble of pathways necessary for cellular energy (ATP) production, which is essential for many cellular functions, including macromolecular biosynthesis, solute transport, signal transduction, chemotaxis, phototaxis, and thermogenesis. The long term goal of this project is to define the cytochrome (cyt) components of the ET pathways, and to understand their structure, mechanism of function and biogenesis (i.e., assembly and regulation). Facultative phototrophic bacteria (e.g., Rhodobacter species) provide an excellent model system for eukaryotic organelles. The ET complexes are widespread among living organisms, and their improper function leads to devastating neuromuscular and mitochondrial diseases in humans, and low crop yields in plants. The project will continue biochemical and molecular genetics of ET complexes, focusing on the structure, function, and biogenesis of membrane-bound, multisubunit cyt c complexes (i.e., the ubihydroquinone:cyt c oxidoreductase, or the bc1 complex, and the recently discovered cyt cb oxidase). The specific aims include the isolation and characterization of mutants of the FeS protein ( a subunit of the bc1 complex) and analysis of their revertants to better understand the role this subunit plays in quinol oxidation; purification and characterization of the FeS protein and the two subunit bc1 subcomplex of R. capsulatus; engineering of structurally simpler bc1 complexes to correlate structural flexibility and functional similarities between oxidoreductases; isolation and characterization of new mutants affecting the biogenesis of multisubunit cyt c complexes and incorporation of their heme and iron-sulfur prosthetic groups; and genetic analyses of biogenesis mutants and determination of cellular locations of their gene products. These studies will increase our understanding of the structure and mechanism of function of the bc1 complex, and provide important insights into the biogenesis of membrane-bound multisubunit cyt c complexes that operate during cellular ET, an important biological process which is far from being completely understood, even in bacteria. Insights gained in this simpler system are generally applicable to the structurally more complex and yet functionally similar organelle-derived ET complexes, and are important for the elucidation of the molecular basis of mitochondrial diseases and aging.